In general, wireless communication apparatuses such as mobile phones are equipped with a power amplifier for transmission power control and other purposes. When a wireless communication apparatus executes transmission power control, output power from a power amplifier is specified. The wireless communication apparatus adjusts input power to the power amplifier so that the output power has a specified value. As a result, transmission power from the wireless communication apparatus converges to a desired value, thereby reducing interference with other wireless communication apparatuses and improving reception quality at a communications partner.
A power amplifier is a component that amplifies and outputs power of input signals. For example, a power amplifier has input/output characteristics as illustrated in FIG. 1. Specifically, input power and output power have linearity until the output power reaches predetermined power Pc, and when the output power exceeds the predetermined power Pc, the relation between input power and output power becomes nonlinear. In the following, the region in which the input/output characteristics have linearity (in FIG. 1, the region in which the output power is less than the power Pc) is referred to as “linear region”, and the region in which the input/output characteristics are nonlinear (in FIG. 1, the region in which the output power is equal to or more than the power Pc) is referred to as “nonlinear region”.
Such input/output characteristics of power amplifiers generally vary depending on individuals, and it is difficult to completely match linear regions and nonlinear regions among individual power amplifiers. Accordingly, before wireless communication apparatuses are shipped to market, the wireless communication apparatuses are adjusted to compensate for individual difference in input/output characteristics of power amplifiers. Specifically, input/output characteristics of respective power amplifiers included in wireless communication apparatuses are actually measured, and actual measurement results are stored in memories of the wireless communication apparatuses or other storage devices. Then, when the wireless communication apparatus is used after shipment, transmission power control is executed based on the actual measurement results of input/output characteristics stored in the memory or other storage devices.
Patent Literature 1: Japanese National Publication of International Patent Application No. 2003-520478
Patent Literature 2: Japanese Laid-open Patent Publication No. 2009-284313
Patent Literature 3: Japanese Laid-open Patent Publication No. 2007-200378
Patent Literature 4: Japanese Laid-open Patent Publication No. 2001-308724
However, the method of adjusting power of power amplifiers based on actual measurements has a problem in that it takes a longer time to adjust wireless communication apparatuses before shipment and accordingly manufacturing cost increases. Specifically, the actual measurements of input/output characteristics of power amplifiers involve measuring output power at a plurality of measurement points with different input powers. In this case, in order to obtain precise input/output characteristics, it is preferred to increase the number of measurement points so as to acquire a larger number of correspondence relations between input power and output power. Therefore, the time for measuring output power for individual wireless communication apparatuses is increased, and it takes a long time to adjust power before shipment. In particular, in recent years, a single wireless communication apparatus is capable of communications in a plurality of frequency bands, and input/output characteristics of a power amplifier differ from one frequency band to another. It is therefore considered that the acquisition of input/output characteristics for each frequency band further increases the time for power adjustment.
Furthermore, in order for a wireless communication apparatus to execute transmission power control, a correspondence relation between input power and output power representing actually measured input/output characteristics is stored in a memory of the wireless communication apparatus or other storage devices. In this case, if a larger number of correspondence relations are stored, a larger storage area such as a memory is occupied, and hence a memory having large storage capacity is mounted in the wireless communication apparatus. As a result, there is another problem in that manufacturing cost of the wireless communication apparatuses further increases. As described above, the method of adjusting power of power amplifiers by measuring power at a plurality of measurement points is inefficient, and the manufacturing cost of the wireless communication apparatuses increases. It is thus desired to efficiently adjust power.